The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) is a next-generation campaign aimed at measuring the earth-moon separation with millimeter precision. Doing so requires precision measurements of the time-of-flight of photons between the earth and moon. APOLLO will utilize new technology in the form of avalanche photodiode (APD) arrays to detect and time-tag the lunar return photons. The APD arrays were provided by Massachusetts Institute of Technology, Lincoln Laboratory but with no accompanying electronic circuitry for biasing or reading out the detectors. I describe the design, construction and testing of the electronics to bias the arrays and detect photons. Once a final prototype version of the electronics was developed, I characterized the temporal and spatial response of the detectors at two different wavelengths: 786 nm and 668 nm. A simple model of APD performance was developed and compared reasonably well with the experimental data. This model was used to predict the detector performance at 532 nm---the wavelength used for APOLLO.